Various types of cellular communication systems are known to provide radio telephone service to a large number of mobile subscribers using a relatively small number of frequencies. Such service is provided by dividing a service area into a number of cells and reusing the frequencies in non-adjacent cells. This cellular principle has permitted a large growth in the amount of wireless telecommunications that may be carried over the allocated radio spectrum thus providing significant expansion in the number of wireless communication mobiles. Various different cellular protocols include analog, time division multiple access (TDMA), code division multiple access (CDMA), Global System for Mobile Communications (GSM), and Universal Mobile Telecommunications System (UMTS).
In many wireless communication systems, Home Location Registers (HLRs) and Visitor Location Registers (VLRs) are used to handle mobility management. An HLR contains profile information for each of its mobile subscribers and the address of the current VLRs for each mobile. Each Mobile Switching Center (MSC) has a VLR that tracks mobiles currently receiving service in the serving MSC's coverage area. Whenever a mobile enters an area served by a new VLR and registers there, the latter informs the mobile's HLR of the change in the mobile's location. In addition, the VLR downloads the service profile of the roaming mobile as well as other information necessary for call termination at the mobile. During call delivery, the location and profile information in the HLR is utilized to route incoming calls to the mobile.
An example of a PSTN to wireless system that provides roaming capability between a PSTN and a roaming mobile is shown in FIG. 1. Long distance networks are shown between the PSTN and the home MSC, where the roaming mobile has its home system, and between the home MSC and the serving MSC, where the roaming mobile is currently located, in order to provide roaming capability to a roaming mobile. When roaming, the mobile may be a significant distance away from its home MSC.
An example timing diagram with a signal flow for a PSTN originated call to a roaming mobile is shown in FIG. 2. Once a roaming mobile registers with a serving MSC in the geographical area of the mobile, the mobile is able to receive calls at this location, including calls from the PSTN. When a call from a calling party to the roaming mobile utilizes the PSTN, the initial call setup is performed on a TDM (Time Division Multiplexed) long distance (LD) network. Quite often, a second TDM long distance network, or perhaps the same long distance network in a second call, is utilized to obtain call information and set up the call between the home MSC and the serving MSC. Further, the cellular system operator may not operate its own long distance network, and must pay tolls to long distance network carriers in order to complete the call set-up.
A problem with this call delivery mechanism is that a call may traverse through the TDM long distance network twice, even when the roaming mobile visits the area where the PSTN calling party resides. The same problem manifests itself in a densely populated area where a wireless network serves several local area transport areas (LATAs). This type of call may incur many unnecessary intra-LATA calls. Thus, utilizing long-distance connections to provide a call to a roaming subscriber is both expensive and a traffic burden on long distance networks.
Accordingly, there is a need for a method and apparatus for providing a roaming mobile with access to the PSTN and other networks distant from his home network without causing undue traffic or expense on existing networks.